1. Field of the Invention
The present invention relates to integrated circuit processing equipment, and more particularly, to a wafer handling module for transferring wafers through a processing system with high throughput.
2. Background of the Related Art
Cluster tools are commonly used in the fabrication of integrated circuits. Cluster tools typically include a loadlock chamber for introducing wafers into the system, a central transfer chamber for moving wafers between the loadlock chamber, one or more process chambers and one or more cooldown chambers mounted on the transfer chamber. Typically, either a single blade or a double blade robot is located in the transfer chamber to move wafers between the loadlock chamber, the processing chamber(s), the cooldown chamber(s) and then back into the loadlock chamber. Exemplary cluster tools, robots and wafer handling methods are described in U.S. Pat. Nos. 4,951,601 and 5,292,393, both of which are incorporated herein by reference.
The use of robot arms is a well established manufacturing expedient in applications where human handling is inefficient and/or undesired. For example, robot arms are used in the semiconductor arts to handle wafers between various process steps. Such process steps include those which occur in a reaction chamber, e.g. etching, deposition, passivation, etc., where a sealed environment must be maintained to limit the likelihood of contamination and to ensure that various specific processing conditions are provided.
Current practice includes the use of robot arms to load semiconductor wafers from a loading port into various processing ports within a multiple chamber reaction system. The robot arm is then employed to retrieve the wafer from a particular port after processing within an associated process chamber. The wafer is then shuttled by the robot arm to a cooldown chamber and then a next port for additional processing or back into the loadlock chamber. When all processing within the reaction system is complete, the robot arm returns the semiconductor wafer to the loading port and a next wafer is placed into the system by the robot arm for processing. Typically, a stack of several semiconductor wafers is handled in this manner during each process run.
In multiple chamber reaction systems, it is desirable to have more than one semiconductor wafer in process at a time. In this way, the reaction system is used to obtain maximum throughput. In the art, a robot arm used in a reaction system must store one wafer, fetch and place another wafer, and then fetch and place the stored wafer. Although this improves use of the reaction system and provides improved throughput, the robot arm itself must go through significant repetitive motion.
One way to overcome the inefficiency attendant with such wasted motion is to provide a robot arm having the ability to handle two wafers at the same time. Thus, some equipment manufacturers have provided a robot arm in which the two carrier blades are rotated about a pivot point at the robot wrist by a motor with a belt drive at the end of the arm. In this way, one wafer may be stored on one carrier while the other carrier is used to fetch and place a second wafer. The carriers are then rotated and the previously stored wafer may be placed as desired. Such a mechanism is rather complex and requires a massive arm assembly to support the weight of a carrier drive located at the end of an extendible robot arm. For example, three drives are usually required for a system incorporating such a robot arm: one drive to rotate the arm, one drive to extend the arm, and one drive to rotate the carriers. Thus, any improvement in throughput as is provided by such a multiple carrier robot arm comes at a price of increase cost of manufacture, increased weight and power consumption, and increased complexity and, thus, reduced reliability and serviceability.
Another approach to providing a multiple carrier robot arm is to place two robot arms coaxially about a common pivot point. Each such robot arm operates independently of the other and improved throughput can be obtained through the increased handling capacity of the system, i.e. two arms are better than one. However, it is not simple to provide two robot arms for independent operation about a common axis. Thus, multiple drives and rigid shafts must be provided, again increasing the cost of manufacture and complexity while reducing reliability.
The various processes which are performed on the various wafers, may involve different time periods with which to perform the process. Therefore, some wafers may remain in a chamber for a short period of time after processing is completed before they are moved into a subsequent process chamber because a wafer is still being processed in the process chamber to which it is to be moved. This causes a backup of wafers which can cause a decrease in throughput of wafers in the system.
In addition to varying process times, another factor which must be considered is the time needed to cool down individual wafers following processing. Typically, along with process chambers, one or more cool down chambers are positioned adjacent to or mounted on the transfer chamber. Wafers are periodically moved into a cool down chamber to enable wafer cooling following processing. In addition, most wafers visit the cool down chamber before they are moved back into the loadlock chamber and removed from the system. As a result, the wafer robot must move wafers into and out of a cool down chamber which adds to the number of movements a robot must make in order to process a number of wafers. Additionally, incorporation of one or more cooldown chambers occupies positions on the transfer chamber where a process chamber could be positioned. Fewer process chambers can result in lower throughput of the system and increases the cost of each wafer processed.
Therefore, there remains a need for a wafer handling module which can increase throughput of wafers while also providing a station in which wafers can be cooled. It would be desirable if the wafer handling module could be used in presently available transfer chambers and systems so that the systems need not be redesigned.